If a special file (block, char, pipe etc) resides on an
xfs filesystem, platform_test_xfs_[fd|path] will return
true, but a subsequent xfsctl will fail, because the file
operations to support the xfs ioctls are not set up on such
files (see i_fop assignments in xfs_setup_inode()).

From the xfsctl manpage it's pretty clear that these functions
are supposed to return true iff a subsequent xfsctl can be
handled, so it makes sense to exclude special files.

This was showing up in xfstest generic/306, which creates
the dev/null block device on an xfstest an tries to pwrite
to it with xfs_io - which emitted a warning when the xfsctl
trying to get geometry failed.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---

diff --git a/include/linux.h b/include/linux.h
index 5bb91cd..502fd1f 100644
--- a/include/linux.h
+++ b/include/linux.h
@@ -34,20 +34,38 @@ static __inline__ int xfsctl(const char *path, int fd, int cmd, void *p)
 	return ioctl(fd, cmd, p);
 }
 
+/*
+ * platform_test_xfs_*() implies that xfsctl will succeed on the file;
+ * on Linux, at least, special files don't get xfs file ops,
+ * so return 0 for those
+ */
+
 static __inline__ int platform_test_xfs_fd(int fd)
 {
-	struct statfs buf;
-	if (fstatfs(fd, &buf) < 0)
+	struct statfs statfsbuf;
+	struct stat statbuf;
+
+	if (fstatfs(fd, &statfsbuf) < 0)
+		return 0;
+	if (fstat(fd, &statbuf) < 0)
 		return 0;
-	return (buf.f_type == 0x58465342);	/* XFSB */
+	if (!S_ISREG(statbuf.st_mode) && !S_ISDIR(statbuf.st_mode))
+		return 0;
+	return (statfsbuf.f_type == 0x58465342);	/* XFSB */
 }
 
 static __inline__ int platform_test_xfs_path(const char *path)
 {
-	struct statfs buf;
-	if (statfs(path, &buf) < 0)
+	struct statfs statfsbuf;
+	struct stat statbuf;
+
+	if (statfs(path, &statfsbuf) < 0)
+		return 0;
+	if (stat(path, &statbuf) < 0)
+		return 0;
+	if (!S_ISREG(statbuf.st_mode) && !S_ISDIR(statbuf.st_mode))
 		return 0;
-	return (buf.f_type == 0x58465342);	/* XFSB */
+	return (statfsbuf.f_type == 0x58465342);	/* XFSB */
 }
 
 static __inline__ int platform_fstatfs(int fd, struct statfs *buf)

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